Effect of adding yeast, Saccharomyces cerevisiae, to a diet containing cottonseed meal on plasma biochemical parameters, mineral retention in the body, and mucosal immune parameters in rainbow trout, Oncorhynchus mykiss

Background and Objective: The use of agricultural waste in the diets of aquatic animals contributes to the sustainability of the aquaculture industry and reduces production costs. However, these food sources have some negative effects on fish health. The addition of probiotics to the diet can mitigate these negative impacts. The aim of this study was to investigate the effect of adding yeast, Saccharomyces cerevisiae, to a diet containing cottonseed meal on plasma biochemical indices, mineral stabilization in the body, and mucosal immune indices in rainbow trout, Oncorhynchus mykiss. Materials and Methods: In this study, three diets were prepared: a control diet without cottonseed meal, a cottonseed meal diet containing 15% cottonseed meal, and a cottonseed meal + yeast diet containing 15% cottonseed meal and 108 cfu/g of S. cerevisiae strain Y5052. Fish with an average weight of 31.6 ± 0.33 g were fed these diets for 8 weeks with 4 replicates. At the end of the feeding period, plasma biochemical indices, mucosal immune responses, and the levels of phosphorus, calcium, and magnesium in the muscle and vertebrae of the fish were determined. Results: The dietary treatments had no significant effect on the activity of aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase, urea in plasma, or on the levels of magnesium in muscle and vertebrae or calcium in muscle. The addition of yeast to the diet resulted in a decrease in alanine aminotransferase activity and plasma creatinine concentration, as well as an increase in phosphorus and calcium levels in the vertebrae and an increase in phosphorus in the muscle of the fish. The addition of cottonseed meal to the diet increased peroxidase and protease activity in the mucosal skin, and the addition of yeast significantly increased these indices compared to the cottonseed meal treatment. Alkaline phosphatase activity in the mucosal skin was higher in the cottonseed meal and cottonseed meal + yeast treatments compared to the control. Conclusion: A 15% level of cottonseed meal in the diet does not have a negative effect on plasma biochemical indices, mineral stabilization in the body, or mucosal immune indices in rainbow trout. The addition of S. cerevisiae strain Y5052 to the cottonseed meal diet at a concentration of 108 cfu/g is recommended to enhance liver and kidney health, increase phosphorus and calcium stabilization, and improve mucosal immune strength.